Ferg
A fascinating tale, for sure, but the danger probably doesn't exist in a
Europa! The difference in cruise and stall speeds is so great that one
would have to be unconscious not to notice...
Tom
beecho@pw-x.com
-----Original Message-----
From: forum-owner@europaclub.org.uk
Subject: A short word at altitude
Cheers,
I see some discussion of Altitude Hold phase of Flight
control
management. While I am in no position to question builders/fliers on
their
experience, I feel it imcumbent to mention it if those unaccustomed to
auto-control are contemplating its installation.
The one phase of 'altitude hold' deserves careful
consideration.
In modern transport aircraft, this phase by itself is inherently unsafe,
unless Airspeed Control is also imposed. While it's obvious that we
don't
want to hold altititude 'til the airspeed loss induces a cruise wing
stall -
it's happened - it IS possible that in this phase other distractions can
make it happen.
Even in modern transports (the L-1011 was most advanced at
the
time), the failure to monitor airspeed and guard against stall can be
induced without warning. In the case of the TriStar, very often the
aircraft
was forced to climb higher for overriding reasons than ideal, which put
it
within so many knots of stall, and of Mach limits. Unforecast turbulence
knocked the auto-pilot down a notch to permit it to smooth
outcorrections in
airspeed and height to play each against the other for a smoother
flight.
However, it knocked the auto-throttles off as well - so we were
particularly
sensitive to stall and Mach. An onboard diversion occurred which (only
for
seconds) took attention of one away from the 'watch' and the aircraft
slowed
to below minimum airspeed. Immediately, the descent in pre-satll was
arrested, but the recovery was reallly delicate, and height was
sacrificed
for speed during power application. This cautionary manoeuvre was not
best
described in the manual. It was changed .........
While over 35000 approaching Iceland westbound, and facing
200knot winds (mechanical trubulence at that height and oscillating up-
and
down-drafts exceeded 2000 fpm) are rare events, it proves that not all
conditions are covered - and altitude-hold can be a fool's paradise
under
rare circumstances.
Thought I should share the idea.............
Cheers, Ferg
PS ....guess what I mean is - if the alt hold is 'on', make sure the
hand is
on the trhottle, the eye on the speed..........
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